Cathode ray tube system with strip chart recorder display format

ABSTRACT

A time variant measured variable is graphically displayed in moving strip chart format on a cathode ray tube. During a scan line the electron beam is intensity modulated at a position on the scan line whith represents the magnitude of the measured variable at a given time. The intensity of the electron beam at positions in successive scan lines is similarly intensitymodulated to produce a trend line representing the magnitude of the variable along the strip chart format. During the scanning of a subsequent raster frame, a new data value of the measured variable is displayed at a selected position at an edge of the viewing area of the strip chart format in thwe location previously occupied by the next sequential value and the older data values are simultaneously displaced. The oldest data value is deleted from the format. During a raster scan the electron beam is modulated at different intensity levels to produce chart lines and time lines on the strip chart format. During each scan line the electron beam may be turned on between a reference position and the position at which the measured variable is recorded to produce a shaded trend line more readily distinguished from other trend lines on the face of the tube. In a modification, a color picture tube produces the different intensity traces so that chart lines, time lines and trend lines are all readily distinguishable one from the other.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatus for data display andmore particularly to the display of a measured variable in a movingstrip chart format on a cathode ray tube.

Moving pen strip chart type recorders have been extensively used inindustry to produce representations of measured dependent variables as afunction of an independent variable, usually time. For example, inelectric power generating plants moving pen recorders continuouslymonitor many of the parameters of power generation. The strip chartrecords provide an excellent visual representation of the operation ofthe plant at any given time. It has become common to record two or moremeasured variables on the same strip chart to provide a convenient wayof directly comparing these measured variables one with the other tobetter determine their interrelationships. While the format of analogstrip chart recorders has become widely accepted as a useful displaymedium, the extensive use of strip chart recorders has attendantproblems.

Strip chart recorders produce a large amount of records and quite oftenit is only portions of these records produced in short time intervalswhich need to be studied. Further, it is only possible to record alimited number of measured variables on a single strip chart recordwithout confusion. Often, two or more measured variables which theoperator wishes to compare are not recorded on the same strip chart. Infact, if a large number, such as 100, measured variables are beingrecorded, the chances of two measured variables, which are desired forcomparison, appearing on one strip chart are small.

Another disadvantage of the extensive use of strip chart recorders iscaused by the necessary physical distance separating the recorders. Inorder to observe all of the measured variables, it is necessary for theoperator to move from one strip chart recorder to another.

Finally, of course, strip chart recorders have the disadvantage ofmoving mechanical elements, such as the recorder pen. The movement ofmechanical elements places an inherent limit on the speed of response,and accuracy of a moving pen strip chart recorder.

One example of a strip chart recorder is shown in U.S. Pat. No.3,389,397--Lex et al.

Recently, cathode ray tubes have been extensively used for graphicaldata display. These devices avoid the problems of moving mechanicalelements which are present in strip chart recorders. Refer for exampleto "A Color-Television Graph Plotter for Digital Computers," Claude A.Wiatrowski, Computer Design, April 1970, pages 133-136. This articledescribes the display of graphs in multiple colors on a cathode raytube. "Drum and Scope Unit Plots Plant Variables," John Werme, ControlEngineering, November 1964, Page 109, describes the display of a processvariable on an oscilloscope type display screen. While graphic displaysystems of the foregoing type are extensively used in many applications,they are not suitable for use as a replacement for strip chart recordersin the monitoring of measured variables of industrial processes. As onereason, they are not capable of displaying the measured variables in aformat to which operators have become accustomed and which format isparticularly convenient for the monitoring of these measured variables.

SUMMARY OF THE INVENTION

In accordance with this invention a measured dependent variable isdisplayed in moving strip chart format on a cathode ray tube. Therelationship between one or more measured variables, and anothervariable, usually time, is displayed as an erasable record on cartesiancoordinates.

In carrying out the invention the electron beam is intensity modulatedat positions in the scan lines of the raster frames which represent themagnitude of the measured variable. For some selected subsequent rasterframes the data values are displaced with respect to the scan lines. Atleast one new data value is added at one extreme of the display and atleast one data value at the other extreme is deleted. In this manner, adisplay is obtained of a trend line representing the measured dependentvariable as a function of the independent variable, in this instancetime. In this manner a moving display of the measured variable as afunction of time is presented in a format which closely resembles thatof a moving strip chart recorder.

In accordance with another important aspect of this invention, shadingis provided for one or more of the trend lines. In carrying this out,the electron beam is intensity modulated between a reference positionand the position representing the magnitude of the measured variable oneach scan line. In this manner, the screen is brightened between areference line and the trend line. This has several advantages. Whenmore than one trend line is displayed, the trend line with shading canbe more easily distinguished from other trend lines. Also, the shadingclarifies the time sequence of widely separated data values and theshading makes it easier to perform a visual interpolation on rapidlychanging data values. Finally, the shaded trend line gives a visualimpression of the value of the time integral of the measured variable.

In accordance with another aspect of this invention, scale lines andtime lines are displayed with different intensities than the trendlines. This makes the scale lines and time lines more readilydistinguishable from the trend lines.

In accordance with another aspect of this invention, the differentintensities of the trend lines, scale lines and time lines are displayedby different colors on the face of a color cathode ray tube.

The foregoing and other objects, features and advantages of theinvention will be better understood from the following more detaileddescription, appended claims and drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a display produced by this invention;

FIG. 2 is a block diagram of the system;

FIGS. 3A-3D are representations of oscillograms of waveforms depictingthe operation of the system;

FIG. 4 is a representation of the appearance of a display with threetrend lines;

FIG. 5 shows the source of clock pulses and the counter;

FIG. 6 shows logic circuitry for producing different levels of thebrightness signal;

FIG. 7 shows the shift register;

FIG. 8 shows the data counters;

FIG. 9A shows the update flip flop;

FIG. 9B shows the interlace gates;

FIG. 10 shows the shift register control circuit;

FIG. 11 shows the delay line shift flip-flop;

FIG. 12 shows the shading switches and the logic circuitry for obtainingthe shading signal;

FIG. 13 shows the line counter;

FIG. 14 shows logic for obtaining the blanking signal;

FIG. 15 shows logic circuitry for producing signals, clearing the shiftregister and transfer of data into the shift register;

FIG. 16 shows the circuitry for producing scan line timing pulses;

FIG. 17 shows gates for producing timing and strobe pulses;

FIG. 18 shows inverting gates for producing logical ones; and

FIG. 19 shows a tape recording system which may be used with theinvention.

DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

FIG. 1 illustrates a display produced on the screen of a cathode raytube television monitor by the system of this invention. FIG. 1 is anegative representation of the display which appears on the cathode raytube screen. That is, a very heavy mark on FIG. 1 represents a verybright mark on the television screen, a moderately heavy mark representsa moderately bright mark on the screen and so on. FIG. 1 shows thedisplay of only a single measured variable although more than onevariable can be displayed.

In FIG. 1 the left-hand vertical scale or chart line 11 represents thelowest value the variable is expected or permitted to have, and theright-hand vertical scale line 13 represents the highest value thevariable can have. Other vertical scale lines such as 10 and 12 form alinear chart with which the data marks representing the values of themeasured variable can be compared.

Successive values of the variables are represented by the data markssuch as 14. These marks occur at horizontal positions in each scan lineof the raster field. The position represents the magnitude of themeasured variable at a particular time. For example, the data mark 14depicts a magnitude between 18 and 19 scale units. The series of datamarks forms a trend line.

The most recent value of the variable is represented by the uppermostdata mark 15 and the oldest value displayed is represented by the datamark 16 at the bottom.

The continuous horizontal lines such as 21 are time lines. Each of thetime lines appears in association with a particular data markrepresenting the value of the variable measured at the time representedby the time line. The brightness of the time lines is less than thebrightness of the data marks so that the latter will not be obscured.The vertical time scale represented by these time lines is a measure ofreal time at which the data values of the measured variable were taken.

In FIG. 1, horizontal shading lines such as 22 extend from the verticalleft-hand scale line 11 to each data mark. In this case, the verticalscale line 11 is the reference line. These horizontal lines 22 may beswitched on or off at the option of the viewer to provide shading(actually brightening) of the screen to the left of the trend line.

This shading has several important functions. When more than one trendline is displayed, the trend line with shading can be readilydistinguished from other trend lines. Where successive data values varyin magnitude greatly, as do the data marks 23, 24 and 25, the shadingmakes it very easy to distinguish whether a particular data markrepresents a time earlier or later than that represented by another datamark. In FIG. 1, the shading makes it clear that the data mark 24occurred at a later time than the data mark 25. Also, when the datamarks are rapidly changing as are those between the marks 26 and 25 theshading makes it easier to perform a visual interpolation of the trendline.

The system shown in the block diagram of FIG. 2 generates such adisplay. The system includes a cathode ray tube television monitor 30.This monitor is of a conventional type having an electron beampositioning circuit which scans the electron beam in a raster field ofscan lines. The monitor 30 also has an intensity modulating controlcircuit which is controlled by a composite video signal applied to theinput 31. This composite video signal is in the form of an amplitudemodulated voltage carrying vertical and horizontal synchronizing pulsesand a video signal. The system of this invention generates such acomposite video signal.

A source of clock pulses 32 divides each scan line of the electron beaminto equal time increments. A counter 33 receives clock pulses. Theseclock pulses are decoded by the gating and decoding circuitry 34 whichgenerates signals for intensifying the brightness of the cathode rayscreen at selected positions on each scan line. For example, the gatingcircuit 34 produces signals on the lines 35-37 at predetermined countintervals. These outputs (subsequently referred to as a second output)produce the scale lines, for example, the scale lines 10, 11 and 12 ofFIG. 1. The outputs on lines 35, 36 and 37 are combined into thecomposite video signal by the combiner 38.

The gating and decoding circuits 34 also produce horizontal sync andvertical sync pulses which are similarly combined into the compositevideo signal by the combiner 38. The gating and decoding circuit 34 alsoproduces a signal referred to as "data dot dash." This signal modulatesthe intensity of data marks along a trend line. This technique is usefulwhen a plurality of trend lines are displayed in order to distinguishone trend line from another.

The sampled data values of the measured variable are supplied to thesystem of FIG. 2 is conventional binary coding at the terminals labeled"sampled data values." In the system to be described each sampled datavalue is contained in a 10-bit word. A digital data storage devicestores a binary coded serial data stream of these data values. Thisdigital data storage device includes shift register 39 and acousticdelay line 40. The acoustic delay line 40 normally forms a circulatingpath for the data values.

In the system being described there are 465 visible scan lines in araster field. Therefore there are normally 465 data values for eachtrend line circulating in the digital data storage device. The system iscapable of displaying three trend lines. Therefore, there are threeten-bit word data values for each scan line. (Actually 31-bit words areused out of 35 available bit positions, 30 bits being used for the datavalues and 1 bit being used for the time line.)

The data words, or values, circulating to shift register 39 are decodedby circuitry indicated as gates, data counters and decoders 41. At aposition in each scan line, which position is denoted by the data word,a data brightness pulse is produced on the line 42. (The data brightnesspulse is subsequently referred to as a first output signal.) This outputsignal is also combined into the composite video signal by the combiner38.

The gates, data counters and decoders 41 also produce a time linecontrol signal on the output line 43. The time line control signal(subsequently referred to as a third output) is mixed into the compositevideo signal to modulate the intensity of the electron beam at adifferent intensity level to produce the time lines such as the lines 21in FIG. 1.

The data words recirculating in the delay line 40 and circulating toshift register 39 are decoded during a first raster frame to produce one(or more) trend lines. At the beginning of a subsequent raster frame, a31-bit data word representing a new data value is inserted in the streamcirculating in the delay line in the position formerly occupied by thedata word representing the next most recent value of the measuredvariable. The latter is inserted in the place formerly occupied by thenext older data word and so on. In this manner the data storage deviceis updated with each data word being displaced with respect to the scanline on which it was previously displayed. At least one new data valueis added at one extreme of the display and at least one data value isdeleted at the other extreme of the display. The updating function isindicated by the switch 44 in FIG. 2. Normally this switch is in thelower position so that the data words in the stream recirculate from theoutput to the input of the acoustic delay line 40. These data words arealso shifted into the shift register 39 for readout. During an updateoperation the switch 44 is actuated to its upper position. Data valuesthen recirculate from the output of the shift register to the input ofthe delay line. The new value is inserted at the appropriate place inthe bit stream. Now there are 466 data values in the bit stream.

The switch is restored to its lower position when the shift registercontains the data value which previously controlled the last raster lineof the display. This procedure results in 465 values, including one newvalue and lacking one old value, circulating in the delay line,automatically synchronized with the scanning so as to appear on thescreen in the same place as did the old data sequence. The lengtheningof the bit stream caused the data values to be shifted by one positionwith respect to the scan line on which they are displayed.

Summarizing the update, during a first raster field, each data word inthe stream modulates the electron beam during one scan line; the firstword, representing the measured variable at a first time, modulates thefirst scan line; the second word modulates the second scan line and soon. During a subsequent raster field, a new data value, representing themeasured variable at a second time, (either earlier or later), modulatesthe first scan line. All subsequent scan lines are modulated by the datawords which have been shifted in position in the bit stream with respectto the scan lines.

During periodic updating the display on the monitor screen appears tomove downward as if a piece of paper bearing the markings on the screenwere being unrolled and written on at the top and rolled out of sight atthe bottom.

All the operations of the system are under control of the system controlindicated at 45. This control produces blanking pulses to blank theelectron beam during retrace. It also provides clock pulses and loadcontrol pulses to the shift register 39.

OPERATION OF THE SYSTEM

The operation of the system will be apparent from FIGS. 3A-3D which arerepresentations of oscillograms of the waveforms of the composite videosignal and the synchronizing signals. FIGS. 3A through 3C each show thecomposite video signal during the scanning of one scan line. FIG. 3Ashows the pulses, such as 70, which occur at every 10 clock pulses.Pulses such as 71 occur at every 50 clock pulses and pulses such as 72occur at every 100 clock pulses. The height of the pulses 70-72determines the relative intensity of the chart lines.

FIG. 3B shows the composite video signal with the same scan mark pulses,and in addition, it shows a pulse which produces one of the data markson each scan line. The pulse 73 produces a data mark on each scan linerepresenting a measuring value.

FIG. 3C shows the foregoing pulses and additionally shows the signalwhich produces shading between the reference mark pulse 79 and the datamark pulse 73. Note that the composite video signal has an amplitudewhich is the same as the amplitude of the pulse 70 during the portion ofthe scan line from zero (left-hand edge) to the data mark pulse 73. Thisintensifiers the beam to the same brightness as the ten's chart marks.

FIG. 3D shows the vertical and horizontal sync signals. The time betweenthe points 74 and 75 is one complete frame. At 76 the vertical syncsignal occurs. This causes the electron beam to shift back from the endof the last scan line displayed to the beginning of the first scan linedisplayed on the next frame. The other regularly occurring pulses 77,78shown in FIG. 3D are the horizontal sync pulses which occur at the endof each scan line.

FIG. 4 is an artist's representation of a display in which threemeasured variables are displayed as the trend lines 50,51 and 52. Thedisplay of FIG. 4 has 100 chart lines but the specific system beingdescribed is also capable of producing a 50-line display.

The chart lines such as 53,54 and 55 in FIG. 4 are produced at every tentime increments, that is, ten clock pulses. The lines 53,54 and 55 andother similar lines are intensified to the lowest level of brightness.At every 50 time increments a line such as the line 56 is intensified toan intermediate level of brightness. At every 100 time increments ascale line such as 57 is intensified to a high level of brightness. Thedata marks making up the trend lines 50-52 are intensified to a fourth,highest level of brightness. In FIG. 4 the shading indicated byreference numeral 58 is at the same intensity level as the scale lines53-55. The shading is represented in FIG. 4 by diagonal and verticalcross hatching which is not present on the screen of an actual display.

DETAILED DESCRIPTION OF THE SYSTEM

A detailed schematic of the system of FIG. 2 is shown in FIGS. 5-18.These figures do not show in detail the conventional television monitor30. In the specific embodiment being described it is a CONRAC Model CQF17/1024/SP television monitor which displays 60 frames per second. Eachraster frame has a nominal 513 scan lines. Of these 513 lines, 465 linesare visible and 48 scan line times are allowed for vertical flyback.

The acoustic delay line is a Tyco Digital Devices 319E-2-83magnetostrictive delay line having a delay of 8.333 milliseconds and abit rate of 2.1546× 10⁶ bits per second.

The remainder of the system is depicted in FIGS. 5-18 as executed withlogical elements in which logical zero is represented by ground level,and logical one is represented by a positive signal. The system includesintegrated circuit modules designated, for example, M102 or N707. Mostof these circuit modules contain two or more functional circuitelements. In general a particular functional circuit element isidentified by appending a number designating an output terminal of themodule. Thus, for example, the two of the four elements contained inmodule M102 (top left of FIG. 5) are designated M102-8 and M102-11. Atable at the end of this section, identifies typical components suitablefor use. For example, gate M102-8 identifies one gate of a quad NORgate.

THE SOURCE OF CLOCK PULSES AND THE TIME INCREMENT COUNTER, FIG. 5

In FIG. 5 the source of clock pulses is the quartz crystal clock 32. Thepulses from this clock are applied to a counter including the JKflip-flop stages M101-M302. As indicated these stages provide two divideby 5 counters, two divide by 2 counters, and a divide by 14 counter. Theoutputs of these counter stages are denoted T1, T2, T3 . . . T12 and thecomplement outputs are denoted T2, T3, . . . T12. The outputs areapplied to gating and decoding circuitry shown in FIGS. 6, 10, 14 and16.

THE REPRESENTATION OF DATA MARKS AND CHART LINE MARKS AT DIFFERENTINTENSITIES, FIG. 6

The circuitry of FIG. 6 performs most of the functions indicated by thegating and decoding block 34 in FIG. 2 and it produces the compositevideo signal as indicated by the block 38.

In the following description the system will be described as producing a100-line chart such as that of FIG. 4. The switch S1 can be moved to theupper position to produce a 50-line chart.

The composite video and synchronizing signal is developed across theresistor R6. It is produced by switching on or off the appropriatecombination of gates M406-6, M204-6, M108-6, M208-6 and M108-8. Thisvaries the current in resistor R6 and the voltage at the composite videoand sync terminal.

A. Production of the Synchronizing Level.

The television monitor used in this implementation requires thesynchronizing level to be the most negative excursion of the compositeinput signal. Synchonizing signals, derived by logical decoding of thestates of counter outputs T9, T10, T11 by gate M401 for horizontalsynchronization and of counter outputs T16, T17, T18, T19, T20 and T21by gate M504 for vertical synchronization, cause gate output M406-6to below. Moreover, the CHART BLANK and DATA BLANK signals are always lowduring synchronizing causing gate outputs M204-6, M108-6, M208-6 andM108-8 to also be low. Thus the composite video signal is low, oreffectively ground.

B. Production of the Black Level.

When no synchronizing signal is present, gate output M406-6 is high. Ifthe monitor screen is not to be brightened, as determined by the absenceof chart line, shading line, or data signals, or the absence of theappropriate inverted blanking signal, CHART BLANK or DATA BLANK, gateoutputs M204-6, M108-6, M208-6 and M108-8 are all low. The high state ofgate output M406-6 causes a current flow in R6 sufficient to produce avoltage drop of about 0.3 volts.

C. Production of the Dimmest Visible Level.

At the time when the monitor screen is to be brightened to any level (inorder to display the chart, the time line, the data mark or the"shading") gate M204-6 is made high in response to a low value of any ofthe signals F, I, C or D. In particular, signal F is low whenever thedecoding of counter outputs T1, T4 and T5 indicates that the dimmestfine chart lines are to be displayed. When 204-6 is made high a currentflows in R6 sufficient to provide an additional voltage drop of about0.15 volts. Since the synchronizing pulses are always absent at thesetimes, the latter voltage drop is added to the former one of 0.3 volts,giving a drop in R6 of 0.45 volts when the screen is to be brightened tothe lowest brightness level.

D. Production of Higher Intensity Levels.

Likewise, when the screen is to be brightened to emphasize each fifth ortenth line of the chart, or to cause a time line to be drawn across thedisplay, or to produce a data mark, gate M108 output 6 is made high inresponse to the absence of any of signals I, C or D. In particular,signal I is low whenever the decoding of counter outputs T1, T4, T5 andT6 indicates that each fifth of the chart lines should be displayed, orwhenever the signal TIME LINE is low, indicating that the data should beaccompanied by a time line. When M108 output 6 is high an additionalcurrent flows in R6 to produce, when added to the other currents fromM406 output 6 and M204 output 6, a drop of about 0.6 volts.

When the screen is to be brightened to emphasize each tenth chart line,decoding of counter outputs T1, T4, T5 and T8 causes input C of gateM208-6 to go low and thus the total voltage drop in R6 is brought to0.75 volts.

The system is capable of displaying three separate data marks on eachraster line. When one of these marks is to be displayed at the brightestlevel in the picture, signal D is low, making gate M208-6 high, and oneof the inputs 9 of gate M108-8 is made low, making the output high andbringing the total voltage drop in R6 to about 0.9 volts. These actionsresult from the decoding of all the states of one of the data counters,such as C1, C2, C3, C4, C5, C6, C7, C8, C9 and C10 in FIG. 8, providedthat the switch DISPLAY C is turned ON as shown. The ability to turn theindividual data marks on or off by switches DISPLAY A, DISPLAY B andDISPLAY C aids the operator to identify and interpret the traces.

THE UPDATING CIRCUITRY, INCLUDING SYSTEM CONTROL 45, FIGS. 7-11

FIG. 7 is a detail of the shift register 39 of FIG. 2. Stages 2-10 havebeen deleted and stages 12-20 have been deleted. The deleted stages arein all ways similar to stages 22-30 which have been shown.

FIG. 8 shows the gates, data counters and decoders 41 of FIG. 2. Three10-stage data counters are provided, one for each of the measuredvariables to be displayed. Only the data counter including the stagesN703-N707 has been entirely shown. These 10 stages make up data counterC. The J-K flip-flop stage M406 is the first stage of data counter B andthe flip-flop N-301 is the first stage of data counter A.

FIG. 9A shows the update flip-flop made up of the logic unit M-706 andFIG. 9B shows the logic circuits M604 and 605 which control the delayline interlace. FIG. 10 shows the shift register control circuit.

FIG. 11 shows the delay line shift flip-flop.

The data record displayed consists of 513 35-bit binary words storedserially in the acoustic delay line serial memory 40 (FIG. 2). Analternative implementation of the system would use a set of longsemiconductor shift registers connected serially to have a capacity of465 or more 31-bit words, with appropriate conventional clock, shiftcontrol and refreshing circuits. A third implementation, to perform thesame functions as the other two, would organize the shift registers intothree parallel memory systems, each being a serial memory with acapacity of 465 or more words, two of the systems using 10-bit words andone using 11-bit words. Alternatively, a random access memory with acyclic address system, or a magnetic drum or disc memory can be used.

For convenience and economy the delay line memory has a delay time of81/3 milliseconds, and is operated in the conventional interlaced modeso that each bit is circulated twice through the memory. Every alternatebit is decoded to be used for control purposes at the output.Recirculation to obtain proper interlace is controlled by gates M605-3,M605-6, M604-6 and M604-8, of FIG. 9B. For simplicity, the followingdescription will treat the delay line and its input gating and controlas if it had a delay time of 162/3 milliseconds and no interlacing.

Only the 465 words which appear at the output of the delay line duringthe scanning of the 465 visible lines of the television monitor screenare used to control the display. Also, only 31 of the 35 bits in eachword are used for control.

At all times during operation of the display the delay line data outputis applied to inputs 2 and 3 of the 32-bit long shift register composedof J-K flip-flops N201 through N208 inclusive, N601, N502 through N507inclusive, and N608 of FIG. 7. This shift register is also provided with31 input gates connected to the wires marked BL1-B31 inclusive, throughwhich parallel data are entered from the external data source, acomputer or other digital device. The states of all stages of theregister are available and used to access the data from the delay linefor control of the monitor picture.

During normal operation of the display the delay line data output isalso applied through gates M605-3, M605-6, M604-6, and M604-8 of FIG. 9Bto the delay line data input for recirculation without modification. Inthis mode, as each word appears at the delay line data output, it isclocked into the shift register at the same time it is being fed to thedelay line data input through the interlace gates of FIG. 9B. When theshift register is filled, toward the end of a monitor raster line sweepperiod, pulse H1264 is generated by the decoding of counter states T3,T5, T6, T7, T9, T11 and T12 in gates M205-6, M-304-6, M305-6 and M305-8of FIG. 16 and is applied to gates N303, N305, N604, N605 and N606 ofFIG. 8 to set the data counter stages (for example, N301, N406,N703-N707 and N607-9 of FIG. 4) to states complementary to those of thecorresponding stages of the shift register.

When "update" is called for, data input line BL32 (FIG. 9A) is madehigh. Then through the action of gates M707-8, M707-11, and M706-8, FIG.9, when STROBE A is generated by gate N704-6 (FIG. 17) during the rasterline time just preceding the top displayed line of a monitor frame, theupdate flip-flop, M706-3 and M706-6, is set. Near the end of the 464thraster line of the next frame, gates M605-8 and M608-8 (FIG. 15) dropthe CLEAR DATA S.R. signal briefly to ground about 140 nanoseconds afterthe H1264 pulse has caused transfer of data from the shift register tothe data counters as described above. This resets all stages of theshift register to zero. Early in the sweeping of the 465th line of theframe, gate M606-8 (FIG. 15) generates pulse STROBE B to set the statesof the first 31 shift register stages equal to the states of data inputlines BL1-BL31 (which, of course, represent the new "updated" data).This occurs before any bit of the next data word appears at the D.L.data output. STROBE B also sets the D.L. shift flip-flop, M603-3 andM603-6. (FIG. 11) The resulting change of state of signals S and Schanges the signal paths through gates M605-6, M604-6 and M604-8 (FIG.9B) so that the DATA S.R. OUTPUT of the shift register is connected tothe DELAY LINE DATA INPUT and the DELAY LINE DATA OUTPUT iscorrespondingly disconnected from DELAY LINE DATA INPUT. As aconsequence, the new data word is shifted from the shift register intothe delay line data input while the former first data word (to controlthe data formerly displayed on the top line of the monitor picture) isshifted from the delay line data output to the shift register during thescanning of the bottom displayed line of the monitor picture. Thereafterthe data shift register clock pulses are interrupted by gate M408-3 andflip-flop M407-9 (FIG. 10) until the scanning of the top display line ofthe next monitor frame.

The foregoing is equivalent to throwing the switch 44 (FIG. 2) to theupper position. This inserts the word from the shift register into thedelay line loop.

During scanning of the 465th line of the frame being discussed, gateM706-11 (FIG. 9A) acts to reset the update flip-flop. If another updateis not required immediately, data input line BL32 will have been resetby the data source to ground level before the next STROBE A pulse time.

While the next frame is scanned, during each line scan time the datafrom the shift register output will be shifted into the delay line datainput as data are accepted into the shift register input from the delayline data output, until, late in raster line 464, the delay line shiftflip-flop M-603-3 and M603-6 (FIG. 11) is reset by gate M-603-8. Thischanges signals S and S to their normal states and the signal pathsthrough gates M605-6, M604-6 and M604-8 (FIG. 9B) again connect thedelay line data output directly to the delay line data input. Theforegoing is equivalent to throwing the switch 44 (FIG. 2) back to thelower position while the old "465" word is still in the shift register.Therefore the old "465" word is deleted.

The result of this operation is that the new data word has been put inthe data stream circulating in the delay line in place of the word whichformerly controlled the data presentation for the top line of thedisplay, the data word which controlled the top line has been put inplace of that which controlled the second line, and every other word hasbeen "shifted back" one line time except the last word, which has beeneliminated from the circulating stream.

THE CIRCUITRY FOR APPLYING THE HORIZONTAL TIME LINES

If a time line is required to accompany the representation of a givenset of data points, line BL31, FIG. 7, from the external data source ismade high when the associated data word is entered by the updatingprocess just described. At the time of updating, when signal STROBE B ishigh, this causes the shift register stage N608-5 (FIG. 7) to be set,and thus the 31st bit of the data word entered in the delay line to be a"one."

Whenever a data word has been completely shifted from the delay linedata output into the shift register, shift register state N608-5 will beset if the 31st bit of the data word is a "one," indicating that a timeline accompanies the data. Signal H1264 is briefly made high, openinggate N606-8 (FIG. 8) to set flip-flop N607-9, making signal TIME LINElow, to remain in this state until the next occurrence of HSYNCH towardsthe end of the next raster line. Signal TIME LINE is connected throughgate M306-8, FIG. 6, to make I low, turning on gates M204-6 and M108-6and producing a drop of at least 0.6 volt in R6 during the duration ofthe chart generation period, as defined by the presence of signal CHARTBLANK.

THE CIRCUITRY FOR OBTAINING SHADING

Shading, as implemented in the display system described here, extendsfrom the left-hand chart line to the position of the data markrepresenting a selected one of the three displayed variables. Theoperator may turn on one of three switches to obtain shading of thevariable he has chosen. The three switches are S5, S6 and S7 of FIG. 12.When one of these switches is turned ON, one of the three inputs of gateN805-12 is low, enabling gate N803-11 to pass pulse H1397, which issubstantially coincident in time with the generation of the video signalto produce the left-hand chart line. Thus the flip-flop made up of gatesN806-6 and N806-11 is set, making the SHADING signal low, and throughgates M306-6 and M306-11 (FIG. 6) causing signal F to be low and gateoutput M204-6 to be high. This gives a voltage drop in R6 of 0.45 volts,causing the monitor screen to be brightened to the same level as is usedto mark the fine chart lines.

The bits of the data word which designate the value of the variableselected by the switch will, prior to the occurrence of pulse H1397,have been used to set one of the three DATA COUNTERS of FIG. 8 to theones complement of the data value. Beginning at the time the left-handchart line signal is generated, the DATA CNTR CLOCK pulses incrementeach of the three ten-bit counters. When all the stages of a counterreach the "one" state, the corresponding signal, DATA A, DATA B, or DATAC (FIG. 6) goes high. This signal is passed by one of the gates N804-3,N804-6, or N804-8 (FIG. 12) to reset the flip-flop N806-6 and N806-11,causing the SHADING signal and signal F (FIG. 6) to go high, ending theshading.

OTHER CIRCUITS

FIG. 13 shows the circuitry for producing the vertical flyback.Horizontal sync pulses are counted in a divide-by-513 counter made up ofthe modules M403, M404 and M405. After counting 513 H SYNC pulses theoutputs T15, T16, T17, T18 are applied to the gate N504-8, FIG. 6, toproduce the vertical sync signal. FIG. 14 shows the logic circuitry forproducing the horizontal and vertical blanking pulses and othernecessary signals, including pulses at lines 465 and 513.

FIG. 15 shows the logic circuitry for producing the CLEAR DATA SHIFTREGISTER and the STROBE B pulses. FIG. 16 shows the logic circuitry forproducing pulses H1264, H1268 and H1270 which occur during each scanline at counts of 1264, 1268 and 1270 respectively. FIG. 17 shows thelogic for producing pulse signals U·L465, (L513·H1270) and STROBE A.FIG. 18 shows gates connected to supply logical one states as requiredin the system.

The following list of typical circuit elements is exemplary and is notto be considered limiting of the invention. In the following tabulation,the designations M101, N102, etc., are the same as those used in FIGS.5-18 and also show the locations which these modules occupy in theactual execution of the invention.

    ______________________________________                                        M101      Motorola MC3062 Dual J-K flip-flop                                  M102      Motorola MC3002 Quad 2-input NOR gate                               M103      Motorola MC3015 8-input NAND gate                                   M104      Motorola MC3010 Dual 4-input NAND                                             gate                                                                M105      Motorola MC3026 Expandable Dual 2-wide                                        2-input AND-OR-INVERT                                                         gate                                                                M106      Motorola MC3002 Quad 2-input NOR gate                               M107      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M108      Motorola MC3005 Triple 3-input NAND                                           gate                                                                M201      Motorola MC3061 Dual J-K flip-flop                                  M202      Motorola MC3062 Dual J-K flip-flop                                  M203      Motorola MC3061 Dual J-K flip-flop                                  M204      Motorola MC3010 Dual 4-input NAND                                             gate                                                                M205      Motorola MC3006 Triple 3-input AND gate                             M206      Motorola MC3062 Dual J-K flip-flop                                  M207      Motorola MC3061 Dual J-K flip-flop                                  M208      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M301      Motorola MC3020 Expandable Dual 2-wide                                        2-input AND-OR-INVERT                                                         gate                                                                M302      Motorola MC3061 Dual J-K flip-flop                                  M303      Motorola MC3061 Dual J-K flip-flop                                  M304      Motorola MC3006 Triple 3-input AND gate                             M305      Motorola MC3026 Dual 4-input AND                                              power gate                                                          M306      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M307      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M308      Motorola MC3005 Triple 3-input NAND                                           gate                                                                M401      Motorola MC3025 Dual 4-input NAND                                             power gate                                                          M403      Motorola MC953 Dual J-K flip-flop                                   M404      Motorola MC839 Divide by 16 counter                                 M405      Motorola MC839 Divide by 16 counter                                 M406      Texas Instruments SN-7486 Quad                                                2-input exclusive-OR gate                                           M407      Motorola MC3062 AND input JJ-KK                                               flip-flop                                                           M408      Motorola MC3002 Quad 2-input NOR gate                               M501      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M502      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M503      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M504      Motorola MC3015 8-input NAND gate                                   M505      Motorola MC3002 Quad 2-input NOR gate                               M508      Motorola MC3025 Dual 4-input NAND                                             power gate                                                          M603      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M604      Motorola MC3005 Triple 3-input NAND                                           gate                                                                M605      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M606      Motorola MC3026 Dual 4-input AND                                              power gate                                                          M608      Motorola MC3025 Dual 4-input NAND                                             power gate                                                          M703      Motorola MC3002 Quad 2-input NAND                                             gate                                                                M704      Motorola MC3001                                                     M705      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M706      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M707      Motorola MC3000 Quad 2-input NAND                                             gate                                                                M708      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N101      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N103      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N106      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N107      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N108      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N201      Motorola MC3061 Dual J-K flip-flop                                  N206      Motorola MC3061 Dual J-K flip-flop                                  N301      Motorola MC3061 Dual J-K flip-flop                                  N303      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N305      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N401      Motorola MC3015 8-input NAND gate                                   N402      Motorola MC3002 Quad 2-input NOR gate                               N406      Motorola MC3061 Dual J-K flip-flop                                  N407      Motorola MC3006 Triple 3-input AND gate                             N408      Motorola MC3015 8-input NAND gate                                   N501      Motorola MC3002 Quad 2-input NOR gate                               N503      Motorola MC3061 Dual J-K flip-flop                                  N504      Motorola MC3061 Dual J-K flip-flop                                  N505      Motorola MC3061 Dual J-K flip-flop                                  N506      Motorola MC3061 Dual J-K flip-flop                                  N507      Motorola MC3061 Dual J-K flip-flop                                  N508      Motorola MC3015 8-input NAND gate                                   N601      Motorola MC3061 Dual J-K flip-flop                                  N602      Motorola MC3061 Dual J-K flip-flop                                  N603      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N604      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N605      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N606      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N607      Motorola MC3062 AND input JJ-KK                                               flip-flop                                                           N608      Motorola MC3061 Dual J-K flip-flop                                  N702      Motorola MC3061 Dual J-K flip-flop                                  N703      Motorola MC3061 Dual J-K flip-flop                                  N704      Motorola MC3061 Dual J-K flip-flop                                  N705      Motorola MC3061 Dual J-K flip-flop                                  N706      Motorola MC3061 Dual J-K flip-flop                                  N707      Motorola MC3061 Dual J-K flip-flop                                  N803      Motorola MC3001                                                     N804      Motorola MC3000 Quad 2-input NAND                                             gate                                                                N805      Motorola MC3005 Triple 3-input NAND                                           gate                                                                N806      Motorola MC3002 Quad 2-input NOR gate                               N808      Motorola MC3000 Quad 2-input NAND                                             gate                                                                ______________________________________                                    

MODIFICATIONS OF THE INVENTION

As previously mentioned, the digital data storage device including theshift register and recirculating delay line may be replaced by a randomaccess memory. Such a memory together with an address counter does notrequire the recirculation and shifting of data. Rather, by periodicallyupdating the address counter, the relationship between the counteraddress and the scan lines is merely shifted. While the invention hasbeen described as representing data values at uniform increments oftime, it will be understood that the time increments need not beuniform.

The system actually described includes a chart line, synchronizing andcontrol counter 33 and data counters 41 (FIG. 2). All counters respondto the same clock pulses from the crystal clock 32. Though the twocounters may be preferred, a single counter may be so controlled as toperform the same functions as the two counters.

In the system described, changes in intensity are effected by changes inthe brightness on the display. Another way to effect changes inintensity is by activating different color phosphors on a color TVmonitor. The use of such a color TV monitor is within the scope of thisinvention.

It will be appreciated that the input data words representing themeasured variable can be obtained from a number of sources. It has beencommon to convert measured variables to digital words and to record themon magnetic tape or a magnetic drum for later replay, and if desired,for real time display of the measured variable. A particularly suitablesystem for recording and playing back the measured variables is shown inFIG. 19. This system accepts new data values when available fromexternal digital data source 60. The strip chart display controller 61and the CRT strip chart display 62 of this invention are not essentialto the record mode of operation but may be used, if desired, for realtime monitoring of the data being recorded.

In the record mode, consecutive data words are received and stored inone of the two buffer memories 63 and 64. When a buffer is filled thecontroller 65 starts the tape deck 66. When the tape is up to speed, thebuffer contents are encoded serially-by-bit in a bi-phase code which isself-clocking as required for a single-track digital recording, untilthe buffer contents are completely recorded, when the tape drive isturned off. The codes are thus written on the cassette tape. Thebi-phase code recording is also known as the frequency doubling method.

During writing or recording, further incoming data words are stored inthe other buffer. The words in the other buffer are then encoded andwritten on the tape when this other buffer is filled. Operation isasynchronous, the rate of the data source 60 being limited only by therequirement that filling of one of the buffers 63 or 64 should not becompleted before the content of the previously filled buffer has beenwritten on the tape.

The recording consists of data blocks or "records" spaced to permitstopping and starting of the tape between consecutive records inplayback. In one implementation, each record comprises thirty-two 32-bitdata words. Short (i.e., two-bit long) gaps are provided betweenadjacent data words and are used in playback to minimize propagation oferrors through the data records.

In a modification of the recording method just described, the buffermemory 63 or 64 may be loaded with the data word deleted from thedisplay (referred to above in the section titled "The UpdatingCircuitry" etc., page 18). In this case the tape recording function maybe placed under automatic or manual control, so that the record to beproduced may be "edited" by reference to the data already displayed.

In the playback mode, the tape controller receives a once-per-framesignal (e.g., the VSYNCH pulse in FIG. 6) from the display controller61. This signal is used, either directly or counted-down, as a displayupdate request. In response to each request, the tape controller 65reads a data word out of one of its internal buffers and sets an updatebit which causes the display controller to update the display in thefollowing frame time. When reading of all words in the buffer has beencompleted, the tape controller 65 starts the tape deck, reads anddecodes a data record from the tape, writes this data, serially-by-bit,in the buffer, and then stops the deck. Meanwhile, further updaterequests are being met by reading data words from the second bufferwhich will in turn be written with new data from the tape when readingis completed.

As each bit is read from buffers 63 or 64 in the playback, a logicalzero is written in its place. This "destructive read" causes the datatrace on the strip chart 62 to fall to zero when no new data isavailable to meet update requests (e.g., when the end of a recording isreached). Alternatively, a logical one may be written in place of eachbit. Then the data trace would go offscale to the right and would not bedisplayed when no new data is available.

As in the record mode, operation in the playback mode is asynchronous.The chart advance (i.e., updating) can be stopped at any time by meansof a switch which blocks update requests from the display controller.

The system in FIG. 19 is particularly advantageous because it providesdigital recording of data on a compact and erasable medium and displayof the recorded data in analog strip chart form.

The bi-phase code used in recording on tape permits the data to be readbackwards without confusion. An alternative implementation of the systemof FIG. 19 could permit the tape to be run backward during replay. Thebuffers could be loaded as described above, but each word could beinverted as it is read from the buffer. The display controller wouldalso be modified so that the new data point can be displayed on thelowest visible raster line, and each old data point be shifted one lineup in the display. The data point which formerly appeared on the topvisible raster line would disappear from the strip chart format. In thiscase, the strip chart format will move upward on the display as the tapeis read backward, or downward as the tape is read forward.

A particular advantage of this recording and display system is that thedigital magnetic records are readable automatically, so that therecorded data can be economically and conveniently transferred to adigital computer for analysis, computation, modification, or the like,and the results can if desired be displayed in the familiar strip chartformat.

While particular embodiments have been shown and described, it will beappreciated that other modifications are within the scope of thisinvention.

What is claimed is:
 1. The method of graphically displaying a timevariant, digitally sampled, measured variable in moving strip chartformat on a cathode ray tube system having an intensity modulatedelectron beam which traverses the face of the tube along successive scanlines in a raster frame comprising:a. modulating the intensity of saidelectron beam at a position in a first scan line of a first rasterframe, said position representing the magnitude of said measuredvariable at a first time, b. modulating the intensity of said electronbeam at positions in successive scan lines of said first raster frame,said positions representing the magnitudes of said measured variablesequentially at times one preceding another, to produce a trend linealong said strip chart format representing said measured variable, c.modulating the intensity of said electron beam at a position in saidfirst scan line of a later raster frame, said position representing themagnitude of said measured variable at a second time, d. modulating theintensity of said electron beam at positions in successive scan lines ofsaid later raster frame, said positions representing the magnitude ofsaid measured variable at times prior to said later time, .[.and.]. e.repeating the foregoing modulating steps for some subsequent rasterframes to produce said moving strip chart format .[...]..Iadd., and f.modulating the intensity of said electron beam in each scan line betweena reference position and the position representing the magnitude of saidmeasured variable to produce a display which is brightened between areference line and said trend line to a lower level of brightness thansaid trend line. .Iaddend.
 2. The method recited in claim 1 wherein aplurality of measured variables are displayed in moving strip chartformat on said cathode ray tube system by modulating the intensity ofsaid electron beam in each scan line at a plurality of positions eachrepresenting the magnitude of one of said measured variables at a giventime.
 3. The method recited in claim 1 further comprising:modulating theintensity of said electron beam at the same scale line positions on eachscan line to produce scale lines along said strip chart format, saidelectron beam being modulated at said scale line positions to adifferent intensity than the modulation at positions representing saidmeasured variable so that the scale lines are readily distinguishablefrom said trend line.
 4. The method recited in claim 1 furthercomprising:modulating the intensity of said electron beam in scan linesassociated with particular samples to produce time lines across saidstrip chart format, said time lines being distinguished from said trendline by a different intensity of modulation of said electron beam. .[.5.The method recited in claim 1 further comprising the intensity of saidelectron beam in each scan line between a reference position and theposition representing the magnitude of said measured variable to producea display which is brightened between a reference line and said trendline..].
 6. The method of graphically displaying a moving strip chartformat on a cathode ray tube system having an electron beam whichtraverses the face of the tube along successive scan lines, said stripchart format representing successive values of an independent variable,and a plurality of stored, digitally encoded data signals representingmeasurements of a dependent variable, comprising:a first step ofreceiving data signals corresponding to the independent variable, asecond step of storing said data signals, a third step of counting clockpulses beginning at the time when the electron beam is at a referenceposition, a fourth step of producing for each scan line a first outputsignal when said clock pulse count corresponds to said data signal forthat scan line, a fifth step of modulating said electron beam to a firstintensity as the electron beam is scanned from said reference positionto a position corresponding to said output signal, a sixth step ofmodulating said electron beam to a second intensity at the occurrence ofeach of said first output signals, repeating the foregoing steps for theremaining raster scan lines, and repeating said third through sixthsteps for a later raster frame, the intensity of said electron beambeing modulated in the scan lines of said later raster frame atpositions corresponding to the output signal at times later than thetimes of the output signal for the preceding raster frame, theoccurrence times of said output signal being displaced with respect tothe scan line on which it is displayed on said later raster frame, oneextreme value of said output signal being deleted and one value beingadded at the other extreme.
 7. The method recited in claim 6 whereinsaid system includes a color reproducing cathode ray tube and whereineach of said different intensities is represented by a different coloron the face of said cathode ray tube.
 8. The method recited in claim 6further comprising:a seventh step of producing a plurality of secondoutput signals at predetermined clock count intervals, and an eighthstep of modulating the electron beam to a preselected intensity at theoccurrence of each of said second output signals to produce verticalscale lines along said strip chart format.
 9. The method recited inclaim 8 further comprising:a ninth step of producing a third outputsignal at preselected intervals of said independent variable, a tenthstep of storing said signal produced in the ninth step in propersequence with said data for said dependent variable, and an eleventhstep of modulating the electron beam to another preselected intensity toproduce horizontal time lines on said strip chart format. A graphiccathode ray tube display system for displaying stored digital data of aplurality of measured variables, said system having a raster scan linetype electron beam positioning circuit and intensity modulating controlcircuit comprising:a source of clock pulses dividing said scan line intoequal time increments, counter means for receiving said clock pulsesincluding means for resetting said counter once during each scan line, adigital data storage device for storing data for each of said measuredvariables, the number of data for each variable corresponding to thenumber of displayed scan lines of said cathode ray tube display, meansfor selecting from storage a particular digital data prior to thebeginning of each scan line, means for producing from said counter afirst output when said counter reaches a count corresponding to saidparticular digital data, means responsive to said first output tomodulate the intensity of the electron beam during each scan linethereby producing a trend line representing said measured variable,.[.and.]. means for updating said data storage device after the scanningof all of said scan lines, said data being displaced with respect to thescan line on which it is displayed on a subsequent scanning of said scanlines, one extreme data value being deleted and one data value beingadded at the other extreme.[...]..Iadd., means for producing from saidcounter a second output at the occurrence of a preselected referencecount, a bistable device being set to one of its states upon the earlieroccurrence of said first or second outputs and reset to the other of itsstates upon the later occurrence of said first or second outputsrespectively, and means responsive to the output of said bistable deviceto modulate said beam with a different intensity corresponding to saidreference digital data. .Iaddend.
 11. The system recited in claim 10further comprising:means for producing from said counter a .[.second.]..Iadd.third .Iaddend.output at predetermined count intervals for scalingeach scan line, and means responsive to said .[.second.]. .Iadd.third.Iaddend.output for modulating the intensity of said electron beam at adifferent intensity level to produce scale lines readily distinguishablefrom said trend line.
 2. The system recited in claim 10 furthercomprising:means for producing a .[.third.]. .Iadd.fourth.Iaddend.output during scanning of scan lines corresponding toparticular data, and means responsive to said .[.third.]. .Iadd.fourth.Iaddend.output for modulating the intensity of said electron beam at adifferent intensity level to produce time lines readily distinguishablefrom said trend lines. .[.13. The system recited in claim 10 furthercomprising:means for producing from said counter a fourth output at theoccurrence of a preselected reference count, a bistable device being setto one of its states upon the earlier occurrence of said first or fourthoutputs and reset to the other of its states upon the later occurrenceof said first or fourth outputs respectively, and means responsive tothe output of said bistable device to modulate said electron beam with adifferent intensity between said reference count and said countcorresponding to said particular digital data..].
 14. A graphic cathoderay tube display system for displaying stored digital data of aplurality of measured variables, said system having a raster scan linetype electron beam positioning circuit and intensity modulating controlcircuit comprising:a source of clock pulses dividing said scan line intoequal time increments, a first counter for receiving said clock pulsesincluding means for resetting said counter once during each scan line, adigital data storage device for storing data for each of said measuredvariables, the number of data for each variable corresponding to thenumber of displayed scan lines of said cathode ray tube display, meansfor selecting from storage a particular digital data prior to thebeginning of each scan line, a second counter for producing a firstoutput when said second counter reaches a count corresponding to saidparticular digital data, means responsive to said first output tomodulate the intensity of the electron beam during each scan linethereby producing a trend line representing said measured variable,.[.and.]. means for updating said data storage device after the scanningof all of said scan lines, said data being displaced with respect to thescan line on which it is displayed on a subsequent scanning of said scanlines, one extreme data value being deleted and one data value beingadded at the other extreme.[...]..Iadd., means for producing from saidfirst counter a second output at the occurrence of a preselectedreference count, a bistable device being set to one of its states uponthe earlier occurrence of said first or second outputs and reset to theother of its states upon the latter occurrence of said first or secondoutputs respectively, and means responsive to the output of saidbistable device to modulate said electron beam with a differentintensity between said reference count and said count corresponding tosaid particular digital data. .Iaddend.
 15. The system recited in claim14 further comprising:means for producing from said first counter a.[.second.]. .Iadd.third .Iaddend.output at predetermined countintervals for scaling each scan line, and means responsive to.[.second.]. .Iadd.third .Iaddend.output for modulating the intensity ofsaid electron beam at a different intensity level to produce scale linesreadily distinguishable from said trend line.
 16. The system recited inclaim 14 further comprising:means for producing a .[.third.]..Iadd.fourth .Iaddend.output during scanning of scan lines correspondingto particular data, and means responsive to said .[.third.]..Iadd.fourth .Iaddend.output for modulating the intensity of saidelectron beam at a different intensity level to produce time linesreadily distinguishable from said trend lines. .[.17. The system recitedin claim 14 further comprising: means for producing from said counter afourth output at the occurrence of a preselected reference count, abistable device being set to one of its states upon the earlieroccurrence of said first or fourth outputs and reset to the other of itsstates upon the later occurrence of said first or fourth outputs,respectively, and means responsive to the output of said bistable deviceto modulate said electron beam with a different intensity betweenreference count and said count corresponding to said particular digitaldata..].